Fatty acid distillation



March 3, 1942. v. MILLS 2274802.

FATTY ACID DISTILLATION 4Filed Feb. 26, 1940 'o Condenser-.s L

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ATTORNEYS.

` Patented Mar. 3, 1942 FAT-Traci msTrLLA'rIoN Victor Mills, Cincinnati,Ohio, assignor to The Procter & Gamble Company,

a corporation of Ohio Application February 2c, 1940, serial Np. 320,825

s claims.

This invention relates to a continuous -process for distillinghigherfatty acids from materials 4containing the same, and moreparticularly concerns a process for the dry distillation of suchmaterials, that is, distillation without the use of steam or other addedgaseous medium. This application is related to my pending application,Serial No. 321,306, liled 'February 28,

1940, which is a continuation-impart of application ,Serial No. 245,440,filed December 13, 1938, in which I have described a method for thedistillation of free fatty acids from fatty acid containing materialsinvolving heating the stock to a Ytemperature sulciently high that 'thelatent heat required 'for vaporization of most of the fatty acids iscontained therein, introducing the heated materialinto a hot liquid bodyof undistilled residue contained within a zone maintained at lowabsolute pressure whereupon most of the fre'e fatty acids vaporizesubstantially instantaneously, employing the vapors thus formed to eiectcontinuous circulation of undistilled residue. in accordance with theair-lift principle and/or the ejector principle, continuouslywithdrawing the vapors .from the low pressure zone and condensing same,and continuously withdrawing excess undistilled residue from said zone.To eiect vaporization under these conditions of subs'tantially'all ofthe vapo'rizable fatty acids in a hydrolyzed materialsuch as tallow orgrease, for example, would require preheating the stock to a temperaturein the neighborhood of 650 F. Under such drastic heat treatment the odorof the distillate is very often impaired even though the preheating andsubsequent flashing steps are promptly carried out. Under preferredoperating conditions as described in my related pending applicationabove referred to, the stockis preheated to. a temperature in the rangeof about 550-575 F. whereby 'l5-80% of the distillable fatty acids arevaporized. The unvaporized residue is normally collected and storeduntil a suiiicient quantity has been accumulated and then re-run throughthe apparatus in a manner similar to that used on the original material.The

Cincinnati, Ohio,

terial takes place. Furthermore subsequent separate distillation of theundistilled residue results in a distillate fraction having differentcharacteristics than the original distillate obtained and thereforethere existsa certain amount of fractionation which may be undesirable..Also when the cooled residue is subsequently subjected to distillation aA material amount, of heat must again be added to bring the stocktodistillation temperature.

The vpresent invention is directed toward obtaining the higherpercentage of fatty acid distillate without allowing the undistilledresidue from the first operation to cool down appreciabl or to come incontact with the atmosphere.

In accordance with my invention the hot residue from the firstdistillation step is pumped under vacuum from the first distillationdevice, through a reheater, and then conducted into a secondary stillwhich may be constructed, for example, either separately from theprimary still or within the primary still.

My invention will be more fully understood from the followingdescription taken in conjunction with the appended drawing in whichFigure 1 illustrates diagrammatically one form of distillation apparatuswhich may be used in A control valve 6 to the primary heating' unit 'Isuch as a heat exchanger, thence through pipe 8 into the still 9. Thestill 9 is provided with a prifatty acid additionally removed by thissecondary mary undistilled residue basin I0, a primary .circulating tubeII, open at its' ends I2'and I3, and a primary y baille I4. Theundistilled residue which collects in basin I0 is continuously drawn offthrough pipe I5 by means of -pump I6 and delivered through pipe I1 andcontrol valve I8, secondary heater I9, and pipe 20 into bottom end 2lofthe secondary circulating tube 22 within the secondary basin 23.Secondary baille 24 is employed to accomplish the same purpose asprimary baille I4, which purpose is described in detail below. Secondaryundistilled residue from the secondary basin 23 is conducted by pipe 25'to receiver 26 which may. be continuously or inter- 2'I. Vapor pipe 28conducts the combined fatty acid vapors of the primary and secondarydistillation steps to suitable condensing equipment' not shown. j

The apparatus shown in Figure 2 is essentially the same as that shown inFigure 1 except that the secondary basin 23 is an integral part of asecondary still 29 which is connected to still 9,. by means of asecondary vapor pipe 30.

The apparatus shown in Figure 1, for example, may be operated asfollows: The material to be distilled, containing a substantial -amountof higher free fatty acids,-is drawn from tank 3 and pumped by/ means ofpump 4 through pipe 5 and feed control valve 6 to the primary heater Iwherein" the material is heated to a sui'ciently high temperature sothat the necessary latent heat of vaporization of most of the fattyacids is contained therein. The heated fatty acid ccntaining material isthen conducted through pipe 8 to still 9 which is maintained at anabsolute pressure of about 0.5 inch of mercury orless, such as 0.05 to0.1 inch of mercury, and wherein substantially instantaneousvaporization of most of the fatty acids taires place. As abovedescribed, the still comprises a primary residue basin i in which issubstantially centrally located a primary circulation tube II. Therelative vertical position of this tube is so adjusted that its bottomend l2 is submerged in the undistilled residue in the still basin I0 andthat its top or outlet end I3 is above the s urface of the undistilledresidue. Suitably` located .above the primary circulating tube II is acircular, umbrella-shaped, primarydeection baille I4. As will be notedfrom the drawing, the heated fatty acid material as introduced into thestill is directed upward within the tube Il. Since the fatty acidmaterial is heated sufiiciently to effect substantially instantaneousvaporization of unvaporized fatty acids at the pressure within thestill, fatty acid vapors will immediately form and by the air-liftprinciple and/or the ejector principle will cause flow of undistilledresidue and' fatty acid vaporsup the tube I I and against baille I4.Further expansion of that portion of the fatty acids vaporized in theheat exchanger l also takes place due to the reduced pressure in thestill. The velocity of the mixture of vapor and undistilled residue issuch that as the undistilled residue strikes the baille I4 a curtain ofliquid is formed, which curtain may be directionally controlled by theshape of the baffle. I have found that this curtain is very effective inremoving entrainment ordinarily accompanying ash distillation,probablybecause of the intimate contact of the vapor with the liquidresidue.

Theundistilled residue continues to collect in the basin I0 asdistillation progresses, any excess above the predetermined amount to bekept in the basin for circulation being removed by pump I6 through pipeI and delivered through pipe l1, control valve I8 to the secondaryheater I9 wherein the undistilled residue is reheated so as toincorporate therein suilicient heat for vaporization of fatty acidscontained in said undistilled residue. The heated residue passesthroughpipe 20 and is introduced into the bottom end 2| of the secondarycirculating tube 22 contained in secondary residue basin 23.A As in` thecase of the rst step of the distillation, fatty acids contained in theheated material volatilize and thereby projectan admixture of same withsecondary undistilled residue against the secundistilled residue isformed. The undistilled residue over and above that required forcirculation in the secondary basin 23 is continuously drawn off throughpipe 25 to receiver 26 from which the residue may be pumpedcontinuouslyor intermittently as desired. The fatty acid vapors from the primary andsecondary distillation steps combine within the vaporization zone of thestill 9 and pass through vapor pipe 28 to suitable condensing equipment.

As above described in the case of Figure 2, a complete secondary still29 may be constructed in a manner similar to the construction of still 9except, of course, preferably on a smaller scale. The fatty acidsvolatilized in still 29 in this case pass through vapor pipe 30 andeither may be condensed separately from the vapors of the primarydistillation or may be combined therewith and passed-through the vaporpipe 28 to suitable condensing equipment. The undistilled residue fromthe secondary distillation step is, of course, removed in a mannersimilar to that above described or if desired may again be reheated andsubjected to distillation conditions.

While the above description gives in detail the general aspects of myinvention, improvements such as the following may be incorporated, theessential features of said improvements being diagrammatically shownbydotted lines in the drawing. It is obvious that vaporization of thefatty acids in the fatty-acid-containing mate-l rial requires a certainamount of latent heat which must be available at or above the fatty acidvaporization temperature corresponding to the operating pressure. Anincrease in volume of material being heated without a correspondingincrease in weight of fatty acid to be vaporized makes possible areduction in temperature to which the stock must be heated in order thatit contain sufficient sensible heat to vaporize that fatty acid.Therefore by recirculating a portion of the undistilled residue andthereby diluting the incoming fatty-acid-containing material theadvantages of lower temperatures may be realized. If, however,temperature is not an item of concern and pressure is, then of course,the diluted material may be heated to the same temperature that is usedin operations not employing recirculation, thereby incorporating alarger amount of available heat for-vaporization ofthe free fatty acidsin the mixture and making possible operation at a higher pressure withinthe still.

If it is desired to recirculate a portion of the primary undistilledresidue and thereby realize advantages as above pointed out, then valve40 in pipe 4I returning to the inlet side of the' heater and valve 42 inpipe II leading to the secondary heater may be adjusted to give thedesired amount of recirculation, the4 temperature.

- my invention I do not take the precaution to ally light in color andmay be used to resistance to passage of the stock through the heater,for example, from about 20 pounds to about zero pounds gage pressurewhereby a mixture of superheated liquid and fatty acid vapors are formedbefore introduction into the still proper. This arrangement differs overprior practice of ash distillation and has presented at least twoadvantages. First, the control valve is subjected to throttlingrelatively cool fatty acid containing material rather than hot material,thereby greatly 'reducing the' corrosive action of the fatty acids onthe valve, and, second, some of the fatty acids are permitted tovolatilize on passage through the heat exchanger and thus thetemperature of the material need not be carrie'd as high as would benecessary. if

pressure were applied to prevent any fatty acidv .3 contained in thebasin za and th-admixture is projected upward against the secondarybaille 24, the fatty-acid vapors thus formed combining with .the .fattyacid vapors evolved in the primary dis,-

tillation step and passing off to suitable condensing lequipment throughthe vapor pipe'28. The

fatty acidsv actually vaporized and condensed' amount to approximately95per cent of the stock glycerin to as high degree as possible andthe tionin order to remove substantially all of the free fatty acid containedvtherein. The undistilled residue resulting from this application of myprocess on oils such as palm oil is exceptiondirectly for any suitablepurpose.

4As a specific example of my procedure carried out in accordance withthe method illustrated diagrammatically. in Figure 1, no recirculationbeing employed, impurefatty acids resulting from the hydrolysis oftallow are heated continuously in primary heater I to a temperature ofS-575 F. and are introduced into the lower end I2 of theprimarycirculating tube II.of still 9 which is maintained at a pressureof about 0.08 inch of mercury absolute pressure. Approximately -80 percent of the stock volatilizes immediately and causes circulation of theprimary undistilled residue contained in the basin I0 whereby saidundistilled residue is projected upwardly against the primary baille I4and deflected so as to form a curtain. of undistilled residue outward,downward, and away from the vapor outlet. 'I'he temperature immediatelydrops` due to volatilization of fatty acids and the fatty. acid vaporsat a temperature of about 450 F. pass through the vapor pipe 28 tosuitable condensing equipment. The undistilled residue, which confed tothe still, theA remaining five per cent being undistilled and/orundistillable residue which is continuously drawn off through pipe 25 torecated within the. primary still, since by this ar-l rangement there isless heat loss and the secondary stillneed not be air tight.

'I'he advantages of recirculation as above described may be -exemplifiedas follows. By recirculating primary undistilled residue in amount equalto about thirty-four per cent of the feed of the originalfatty-acid-containing material to the primary circulating tube and byrecirculating about sixty-nine per cent of the feed of primary residueto the secondary circulation tube, the' temperature to which therespectivev feeds should be heated may be reduced to about 515 F. withsimultaneous increase in pressure in thelstill to about 0.16 inch ofmercury. The higher fatty acids with which I am prini cipally concernedare the saturated and unsaturated carboxylic acids occurring invegetable,

animal, or marine fats and oils-and containing mostly from about-ten toabout twenty .c :aibon4 atoms per molecule, such as oleic', linolic,stearic,

palmitic, myristic, lauric, etc. The principal use .of such acids is inthe manufacture of soap and candles. Other impure higher fattyacids-Which are of less common occurrence such as the higher acidsresulting from the oxidation vof parailin may'also be purified bydistillation in accordance with the present invention.

Having thus described my invention, what I claim` and desire to secureby Letters Patent is:

1. A process of continuously distilling at reduced pressure without'theuse -of an added gaseous medium higher fatty acids from a materialrated. in said material to effect substantiallyl instantaneousvaporization of most of the free fatty acids contained therein whensubsequently subjected to said reduced pressure, continuouslyintroducingthe thus heated material into a hot sists of about 20-25 per cent of thestock fed and which likewise has dropped in temperature to approximately450 F., is removed by means of pump I6, reheated in the secondary heaterI9 to 575-590 F., and introduced into the bottom end 2i of the secondarycirculation tube 22 contained within the secondary basin 23. Fatty'acids contained in the heated residue are volatilized, be-j comeadmixed with secondary undistilled residue liquid body of primaryundistilled residue contained within a zone maintained at a pressureless than the average pressure in said heating zone and notsubstantially exceeding 0.5 inch of mercury whereupon most of the freefatty acids I vaporize substantially instantaneously,y employing thevapors thus formed Without the aid of an added gaseous medium to projectsaid residue upwardly against a baiiie to form a directionallycontrolled curtain of undistilled residue, continuously withdrawingexcess undistilled residue Y from said zone, reheating the said excessresidue to incorporate sufficient heat in same tosubstantiallycompletely vaporize the fatty acids contained thereink at the pressurewithin said zone and thereby leave a secondary undistilled residue.continuously introducing the said heated 1 excess residue into a hotliquid body of said secondary undistilled residue and employing thevapors thus formed to project a stream of said secondary undistilledresidue, intimately admixed with said vapors; upwardly against a bafflein a zone at said low pressure so as to form a directionally controlledcurtain of secondary undistilled residue, continuously withdrawing thefatty acid vapors and condensing same and continuously withdrawing saidsecondary undistilled residue',

2. In a process of dry flash distillation of fatty acids including :thestep ofprojecting undistilled residue intimately admixediwith vaporizedfatty acids without the-'aid of an added gaseous medium against a baillein a low pressure distillation zone so as to create a curtain ofundistilled residue, the steps of removing excess residue over and abovethe predetermined amount necessary for the admixture projected.reheating -the removed residue to incorporate suilicient heat in same tovaporize most of the free fatty acids contained therein at low pressureand thereby leave a secondary undistilled residue, continuouslyintroducing said heated residue into ahot liquid.

body of said secondary undistilled residue and employing the vapors thusformed without the aid of an added gaseous medium to project a stream ofsaid secondary undistilled residue intimately admixed with said vaporsupwardly against a ballle in a zone at said low pressure so as to createa curtain of said secondary undistilled residue.

3. The process in accordance with claim 2 in which the vapors from thefirst and second vaporization are combined before being condensed.

4. I'he process in accordance with claim 2, in which the vapors areseparately. condensed.

i 5. The process of claim 2, in which the secondary and primaryvaporizations are conducted within the same distillation zone.

6. The process of claim 2, in which. the secondary and primaryvaporizations are conducted in separate, interconnected zones.

7. A process of subjecting to redistillation an undistilled residue froma primary distillation of a fatty-acid-containing material comprisingheating the undistilled residue to incorporate sucient heat in same tovaporize most of the free fatty acids contained therein at low pressureand thereby leave a secondary undistilled residue, continuouslyintroducing said heated residue into a hot liquid body of said secondaryundistilled residue and employing the vapors thus formed without the aidof an added gaseous medium to project a stream of said secondaryundistilled residue intimately admixed with said vapors upwardly againsta baille in a zone at said low pressure so as to create a curtain ofsaid secondary undistilled residue.

8. A processv of subjecting to redistillation an undistilled residuefrom a primary distillation of a fatty-acid-containing materialcomprising heating the undistilled residue while subjecting same toprogressively decreasing pressure to incorporate sufficient heat in sameto vaporize

